This guide outlines how to enable the built-in VPN service (vpnd) in client versions of OS X, as Apple has neglected to mention (let alone explain) the possibility under non-server editions of OS X. Standard disclaimer applies, as always: You are 100% responsible for your own actions. Using this guide, visiting a link, downloading a program, in short, living, is done entirely at your own risk (and joy).

I. Diagram of Example Network

The domain name and IP addresses above are for example purposes only and will likely differ on your networks.

There are loads of fun things you can do once connected to your VPN, but here's one: if you enable Screen Sharing on your VPN server (System Preferences > Sharing), access it from a connected Mac (and optionally any VNC client) via Cmd+K > vnc://server_ip_or_name.

After 2.4b, iVPN became shareware. Its new homepage can be found here. I decided to avoid the shareware version after reading comments here and here.

The new and vastly superior EasyVPN offers similar functionality to iVPN, but includes Lion support, launchd (as opposed to StartupItem) startup, and a price tag of only $4.99 (versus £14.99 for the current version of iVPN).